It is well known in the art that complexes of nickel with phosphorous-containing ligands are useful as catalysts in hydrocyanation reactions. Such nickel complexes using monodentate phosphites are known to catalyze hydrocyanation of butadiene to produce a mixture of pentenenitriles. These catalysts are also useful in the subsequent hydrocyanation of pentenenitriles to produce adiponitrile, an important intermediate in the production of nylon. It is further known that bidentate phoshite and phosphinite ligands can be used to form nickel-based catalysts to perform such hydrocyanation reactions.
U.S. Pat. No. 3,903,120 discloses a process for preparing zero-valent nickel complexes by reacting elemental nickel with a monodentate phosphorous ligand of the formula PZ3 where Z is an alkyl or alkoxy group, or preferably an aryloxy group. The process uses finely divided elemental nickel and is preferably carried out in the presence of a nitrile solvent. The reaction is carried out in the presence of excess ligand.
U.S. Pat. No. 3,846,461 discloses a process for preparing zero-valent nickel complexes of triorganophosphites by reacting triorganophosphite compounds with nickel chloride in the presence of a finely divided reducing metal which is more electropositive than nickel, and in the presence of a promoter selected from the group consisting of NH3, NH4X, Zn(NH3)2X2, and mixtures of NH4X and ZnX2, where X is a halide. Reducing metals include Na, Li, Mg, Ca, Ba, Sr, Ti, V, Fe, Co, Cu, Zn, Cd, Al, Ga, In, Sn, Pb, and Th, with Zn being preferred.
U.S. Pat. No. 5,523,453 discloses a method of preparing nickel hydrocyanation catalysts containing bidentate phosphorous ligands. Zero-valent nickel compounds that contain ligands that can be displaced by the bidentate phosphorous ligand are a preferred source of nickel. Two such compounds are Ni(COD)2, where COD is 1,5-cyclooctadiene, and (oTTP)2Ni(C2H4), where oTTP is P(O-ortho-C6H4CH3)3.
Pending U.S. application having the Ser. No. 09/994,102 describes a process for producing a catalyst by contacting divalent nickel compounds with reducing agents. In the disclosed process, the nickel compounds are dried prior to introduction to the reactor. The application describes that the rate of catalyst production increases with increasing temperature, but the amount of ligand degradation and byproduct formation also increases. Accordingly, there is a need for a process that allows for high reaction rates, low degradation, and byproduct formation and the advantage of less expensive drying equipment.